The field of rapid prototyping involves the production of prototype polymeric articles and small quantities of functional polymeric parts, directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective laser sintering process and a liquid binder three dimensional printing process. These techniques are similar, to the extent that they both use layering techniques to build three-dimensional articles. Both methods form successive thin cross-sections of the desired article. The individual cross-sections are formed by bonding together adjacent grains of a granular, (i.e., particulate) material on a generally planar surface of a bed of the granular material. Each layer is bonded to a previously formed layer at the same time as the grains of each layer are bonded together to form the desired three-dimensional article. The laser-sintering and liquid binder techniques are advantageous because they create parts directly from computer-generated design data and can produce parts having complex geometries. Moreover, three dimensional printing may be quicker and less expensive than machining of prototype parts or production of cast or molded parts by conventional “hard” or “soft” tooling techniques that can take from a few weeks to several months, depending on the complexity of the item. By contrast, the three dimensional printing process allows one to produce a demonstration prototype or in some instances, a usable part, within hours or days.
An extrusion-based layered deposition system (e.g., fused deposition modeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) is typically used to build a 3D object from a CAD model in a layer-by-layer fashion by extruding a flowable build material, such as a thermoplastic material. The build material is extruded through a nozzle carried by an extrusion head, and is deposited as a sequence of roads on a base in an x-y plane. The extruded build material fuses to previously-deposited build material, and solidifies upon a drop in temperature. The position of the extrusion head relative to the base is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D object resembling the CAD model.
In many instances, it is desirable to be able to construct three-dimensional objects that are of high density or that offer sufficiently high radio-opacity to be able to provide application-satisfactory radioactive or electromagnetic radiation shielding.
It is likewise desirable in other applications to be able to produce articles or prototypes of relatively high density to be able to take advantage of higher density in applications where three dimensional printing is advantageous, scuh as for the production of prototypes or operative articles, particularly where dimensional stability, strength, reliability and manufacturing consistency are beneficial.